Posts Tagged ‘USS Thresher’

Saturday marked the 66th anniversary of Robalo leaving on her final complete patrol (her next one will be the fatal one) and the 47th anniversary of America’s first nuclear submarine disaster.

But first, the Robalo. Sixty-six years ago yesterday, the Robalo pulled up anchor in Fremantle and took off for her second patrol, the first one under Commander Kimmel. This patrol would be safe and successful, but would raise questions in September about the eventual fate of the Robalo.

The Robalo, underway in 1943

Fast forward to 1963. While some WWII diesel boats ARE still in service, the American Navy is quickly replacing them with teardrop-shaped nuclear boats. First the Nautilus in 1954, then the Seawolf III in 1957 (a liquid sodium cooling system that was quickly abandoned) and on an on, developing, improving, tweaking and changing, all under the intense (and some would say, terrifying) eye of Admiral Hymen G. Rickover. Nine years of nuclear submarines and brand new technology in a dangerous and demanding environment without a massive loss.

Until April 10, 1963. The USS Thresher, lead ship of her class, was at sea doing routine exercises. A year earlier, she had been accidentally rammed by a tug boat during another exercise, and had been overhauled, and so was out testing all the new repairs. She was accompanied by the Submarine Rescue Ship Skylark, just in case there were difficulties.

The Thresher, underway from the air. Notice the evolution in twenty years from a submarine like Robalo which was designed to fight and travel on the surface as well as temporarily underwater to the Thresher, which was designed to do everything underwater.

Just before 8 am, the submarine began a dive to her (officially published) test depth of 1300 feet. She descended past a thermocline (see below) which caused her transmissions to be more garbled and difficult to hear. Skylark kept calling Thresher, and, at 9:13 am, heard a very garbled but understandable message: “Experiencing minor difficulty, have positive up-angle, attempting to blow. Will keep you informed.”

The Skylark assured Thresher the sea was empty, in case she had to do an emergency surface. Three minutes later, a garbled message was received, including the phrase “900N” the meaning of which is still unknown. A minute after that, another garbled message, with only one intelligible phrase “…exceeding test depth…” One minute later, the Skylark heard a low-frequency noise. It sounded like an implosion.

That was it. Nothing more was ever heard from the Thresher, though Skylark spent hours calling Thresher, asking her to respond via radio, smoke bomb, or any other means to show they were okay.

So 47 years ago today, the Navy announced the USS Thresher was lost at sea, with all hands, plus 19 civilian observers, a total of 129 people.

Dr. Robert Ballard, who would discover the Titanic a few weeks later (and those discoveries were connected), discovered the remains of the Thresher in 1982. From what was theorized in ’63 and confirmed in the imploded wreckage in ’82, the Thresher likely had a pipe burst in the engine room, flooding it. These pipes were not welded like today’s subs (actually, the Thresher disaster is WHY modern sub pipes and hulls are welded) they were silver brazed, and it was known that there were some problems with some joints, though it was not considered a dangerous enough problem to need to fix.

This photograph is part of Thresher's hull, the white paint seen here used to say "593", the hull number of the Thresher. The Thresher was the lead ship of her class ("Thresher Class Submarines") but following her loss, many people called the class "Permit Class Submarines" after Thresher's next sister.

The water spray probably shorted out some electrical systems, prompting an automatic emergency shutdown of the nuclear reactor. The ship tried to blow her ballast tanks, to surface, but later tests showed ice probably formed in the valves, keeping the ballast tanks water filled. With the Engine Room flooding, the sub eventually sank, went past her crush depth and imploded. She tore herself into six main pieces.

The only mercy might be that when death finally came, it was nearly instantaneous.

Upon discovering the submarine had gone down due to mechanical failure (not Soviet interference) the US Navy instituted the SUBSAFE program, designed to rigorously and obsessively track and document the quality of construction of US Submarines (for example, welds are X-rayed to make sure there are no weak spots or air bubbles that would give way under pressure, and those X-rays are stored in case something happens to the sub) to make sure that slipshod construction never cost another crew their lives again. Such attention to detail is one of the reasons why a submarine is, foot for foot, the most expensive naval vessels to build.

It was a sad end to 129 gallant souls the largest loss of life in a single submarine incident in American History. May they rest in peace.

SO WHAT’S A THERMOCLINE? The top surface of the ocean is repeatedly warmed by the sun by day and cooled at night. The deeper the ocean goes, the cooler and more steady the temperature gets. This does not happen at a steady rate. A Thermocline is a layer in the ocean where the temperature falls more quickly than the layer above and below. Thermoclines are very important for submarines, since they can be used to hide under and help deflect Sonar. As the Thresher story shows, however, thermoclines can work against a submarine.